The car moved uniformly for 2 hours at a speed of 20 m / s, and for the next 3 hours

The car moved uniformly for 2 hours at a speed of 20 m / s, and for the next 3 hours, too, uniformly at a speed of 15 m / s. What is the average vehicle speed.

The average speed of the vehicle along the entire route will be determined by the formula:

Vav = S / t, where S is the entire path that the car has covered, t is time. which it took him.

In the problem statement, two sections of the path with different conditions are given.

S = s1 + s2;

s1 = v1 * t1, where v1 is the speed of the car on the first section of the path, t1 is the time to overcome the first section.

v1 = 20 m / s (or 72 km / h), t1 = 2 hours;

s1 = 72 * 2 = 144 km.

s2 = v2 * t2, where v2 is the speed of the car on the first section of the path, t2 is the time to overcome the first section.

v2 = 15 m / s (or 54 km / h), t2 = 3 hours;

s1 = 54 * 3 = 162 km;

S = 144 + 162 = 306 km;

T = 2 + 3 = 5 hours;

Vav = 306/5 = 61.2 km.

Answer: the average speed of the car along the entire route was 61.2 km / h